Circadian variation in swim performance

• Published in: Journal of applied physiology (1985) Vol. 102; no. 2; pp. 641 - 649
• Main Authors: Kline, Christopher E, Durstine, J. Larry, Davis, J. Mark, Moore, Teresa A, Devlin, Tina M, Zielinski, Mark R, Youngstedt, Shawn D
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01-02-2007; American Physiological Society
• Subjects: Adult; Affect - physiology; Biological and medical sciences; Biology; Body Temperature - physiology; Circadian rhythm; Circadian Rhythm - physiology; Data Interpretation, Statistical; Energy Intake - physiology; Fatigue - physiopathology; Female; Fundamental and applied biological sciences. Psychology; Humans; Male; Psychometrics; Sleep - physiology; Swimming; Swimming - physiology; Swimming - psychology; Temperature; Sport; Vertebrata; Swimming(sport); Mammalia; Physical performance; Body temperature; body temperature rhythm; Biological rhythm; Swimming; ultra-short sleep-wake cycle; Sleep wake cycle; Circadian rhythm
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00910.2006

Department of Exercise Science, Arnold School of Public Health, University of South Carolina, Columbia, South Carolina
Submitted 17 August 2006
; accepted in final form 1 November 2006
Previous findings of time-of-day differences in athletic performance could be confounded by diurnal fluctuations in environmental and behavioral "masking" factors (e.g., sleep, ambient temperature, and energy intake). The purpose of this study was to examine whether there is a circadian rhythm in swim performance that is independent of these masking factors. Experienced swimmers ( n = 25) were assessed for 50–55 consecutive hours in the laboratory. The swimmers followed a 3-h "ultra-short" sleep-wake cycle, involving 1 h of sleep in darkness and 2 h of wakefulness in dim light, that was repeated throughout the observation. The protocol distributes behavioral and environmental masking factors equally across the 24-h period. Each swimmer was scheduled to perform six maximal-effort 200-m swim trials that were distributed equally across eight times of day ( n = 147 trials). Each trial was separated by 9 h. A cosine fit of intra-aural temperature data established the time of the lowest body temperature (T min ). Swim performances were z -transformed and compared across the eight times of day and across twelve 2-h intervals relative to T min . Analysis of covariance, controlling for trial number, revealed a significant ( P < 0.001) pattern in swim performance relative to environmental and circadian times of day. Performance peaked 5–7 h before T min ( 2300) and was worst from 1 h before to 1 h after T min ( 0500). Mean swim performance was 169.5 s; circadian variation from peak to worst performance was 5.8 s. These data suggest a circadian rhythm in athletic performance independent of environmental and behavioral masking effects.
body temperature rhythm; swimming; ultra-short sleep-wake cycle
Address for reprint requests and other correspondence: S. D. Youngstedt, Dept. of Exercise Science, Arnold School of Public Health, Univ. of South Carolina, 1300 Wheat St., Rm. 102, Columbia, SC 29208 (e-mail: syoungstedt{at}sc.edu )